Implantable medical device with a dual power source

ABSTRACT

An implantable medical device includes a control circuit for controlling the operation of the device and for obtaining physiological data from a patient in which the medical device is implanted. The implanted device also includes a communication circuit for transmitting the physiological data to an external device. A first power source is coupled to the control circuit and provides power to the control circuit. A second power source is coupled to the communication circuit and provides power to the communication circuit.

PRIORITY CLAIM

[0001] This Application is a continuation-in-part of U.S. patentapplication Ser. No. 09/870,097 (P-7586, filed May 30, 2001, entitled“Implantable Medical Device With a Dual Cell Power Source,” which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a power source for animplantable medical device, and more particularly, the present inventionrelates to a dual cell power source for optimizing implantable medicaldevice performance.

[0003] A variety of different implantable medical devices (IMD) areavailable for therapeutic stimulation of the heart and are well known inthe art. For example, implantable cardioverter-defibrillators (ICDs) areused to treat those patients suffering from ventricular fibrillation, achaotic heart rhythm that can quickly result in death if not corrected.In operation, the ICD continuously monitors the electrical activity of apatient's heart, detects ventricular fibrillation, and in response tothat detection, delivers appropriate shocks to restore normal heartrhythm. Similarly, an automatic implantable defibrillator (AID) isavailable for therapeutic stimulation of the heart. In operation, an AIDdevice detects ventricular fibrillation and delivers a non-synchronoushigh-voltage pulse to the heart through widely spaced electrodes locatedoutside of the heart, thus mimicking transthoratic defibrillation. Yetanother example of a prior art cardioverter includes thepacemaker/cardioverter/defibrillator (PCD) disclosed, for example, inU.S. Pat. No. 4,375,817 to Engle, et al. This device detects the onsetof tachyarrhythmia and includes means to monitor or detect progressionof the tachyarrhythmia so that progressively greater energy levels maybe applied to the heart to interrupt a ventricular tachycaria orfibrillation. Numerous other, similar implantable medical devices, forexample a programmable pacemaker, are further available.

[0004] Regardless of the exact construction and use, each of theabove-described IMDs generally include three primary components: alow-power control circuit, a high-power output circuit, and a powersource. The control circuit monitors and determines various operatingcharacteristics, such as, for example, rate, synchronization, pulsewidth and output voltage of heart stimulating pulses, as well asdiagnostic functions such as monitoring the heart. Conversely, thehigh-power output circuit generates electrical stimulating pulses to beapplied to the heart via one or more leads in response to signals fromthe control circuit.

[0005] The power source provides power to both the low-power controlcircuit and the high-power output circuit. As a point of reference, thepower source is typically required to provide 10-20 microamps to thecontrol circuit and a higher current to the output circuit. Dependingupon the particular IMD application, the high-power output circuit mayrequire a stimulation energy of as little as 0.1 Joules for pacemakersto as much as 40 Joules for implantable defibrillators. In addition toproviding a sufficient stimulation energy, it is desirable that thepower source possess a low self-discharge to have a useful life of manyyears, and that it is highly reliable, and able to supply energy from aminimum packaged volume.

[0006] Suitable power sources or batteries for IMD's are virtuallyalways electrochemical in nature, commonly referred to aselectrochemical cells. Acceptable electrochemical cells for IMDstypically include a case surrounding an anode, a separator, a cathodeand an electrolyte. The anode material is typically a lithium metal or,for rechargeable cells, a lithium ion containing body. Lithium batteriesare generally regarded as acceptable power sources due in part to theirhigh energy density and low self-discharge characteristics relative toother types of batteries. The cathode material is typically metal-based,such as silver vanadium oxide (SVO), manganese dioxide, etc.

[0007] In some cases, the power requirements of the output circuit arehigher than the battery can deliver. Thus, it is common in the prior artto accumulate and store the stimulating pulse energy in an output energystorage device at some point prior to the delivery of a stimulatingpulse, such as with an output capacitor. When the control circuitindicates to the output circuit that a stimulating pulse is to bedelivered, the output circuitry causes the energy stored in the outputcapacitor to be applied to the cardiac tissue via the implanted leads.Prior to delivery of a subsequent stimulating pulse, the outputcapacitor is typically recharged, with the time required for the powersource to recharge the output capacitor being referred to as the “chargetime”.

[0008] Regardless of whether an output capacitor(s) is employed, oneperceived drawback of currently known therapeutic pulsing IMDs is thatthey often have to be replaced before their battery depletion levelshave reached a maximum. When an IMD's output capacitor is beingrecharged, there is a drop in battery voltage due to the chargingcurrent flowing through an inherent battery impedance. Although thisvoltage drop may not be significant when the battery is new or fresh, itmay increase substantially as the battery ages or is approachingdepletion, such that during a capacitor recharging operation, thevoltage supply to the control circuit may drop below a minimum allowablelevel. This temporary drop can cause the control circuit to malfunction.The IMD may be removed and replaced before any such malfunctions occur,even though the battery may still have sufficient capacity to stimulatethe heart. Simply stated, the rate capability of currently availablelithium-based cells is highly dependent upon time or depth-of-dischargeas the cell develops high internal resistance over time and/or withrepeated use. For IMD applications, this time or depth-of-dischargedependence limits the battery's useful life.

[0009] One solution to the above-described issue is to provide twobatteries, one for charging the output circuit or capacitor and aseparate battery for powering the control circuit. Unfortunately, therelative amounts of energy required by the device for the control andcharging/output circuitry tend to vary from patient to patient. Thecapacity of the battery to power the control circuit can only beoptimized with regard to one patient profile. Thus for other patients,one battery may deplete before the other, leaving wasted energy in thedevice. An example of such a system is disclosed in U.S. Pat. No.5,614,331 to Takeuchi et al.

[0010] An additional, related concern associated with IMD power sourcesrelates to overall size constraints. In particular, in order to providean appropriate power level for a relatively long time period (on theorder of 4-7 years), the power source associated with the high-poweroutput circuitry typically has a certain electrode surface area toachieve the high-rate capability. Due to safety and fabricationconstraints, the requisite electrode surface area can be achieved withan increased cell volume. The resulting cell may satisfy outputcircuitry power requirements, but unfortunately may be volumetricallyinefficient. Even further, recent IMD designs require the power sourceto assume a shape other than rectangular, such as a “D” or half “D”contour, further contributing to volumetric inefficiencies.

[0011] In general terms, then, currently available electrochemical celldesigns, especially Li/SVO constructions, may satisfy, at leastinitially, power requirements for the output circuitry. The inherentvolumetric inefficiencies of these cells, however, dictates anend-of-life point at which less than the cell's useful capacity has beenused. Once again, currently available cells exhibit an output circuitrycharge time that is highly dependent upon time of use ordepth-of-discharge. Over time, the cell's impedance increases, therebyincreasing the resulting charge time. Virtually all IMDs have a maximumallowable charge time for the output circuitry. Once the cell's chargetime exceeds the maximum allowable charge time, the IMD may be replaced.The volumetrically inefficient cell may quickly reach this maximumcharge time, even though a large portion of the cell's capacity remainsunused (on the order of 40% of the useful capacity). Thus, regardless ofwhether the power source incorporates one or two cells, the resultingconfiguration is highly inefficient in terms of the high-rate battery'suseful capacity.

[0012] Manufacturers continue to improve upon IMD construction and sizecharacteristics. To this end, currently available power source designsare less than optimal. Therefore, a need exists for an IMD power sourcehaving superior space-volumetric efficiencies and a higher energydensity, without a proportional increase in charge time.

[0013] Yet another issue associated with IMD power sources involves theuse of a wireless transceiver to communicate IMD data with an externaldevice. The data communicated by the IMD may include physiological datarelated to the patient in which the IMD is implanted. For example, ifthe IMD is a pacemaker or cardioverter/defibrillator, the physiologicaldata may include electric cardiac signals obtained from electrodesimplanted within the patient's heart as previously discussed. Theexternal device with which the IMD communicates this physiological datamay include a computer, for example, that monitors and/or processes thephysiological data that is received from the IMD.

[0014] The IMD may also communicate data related to its performance,such as the intensity level in which it delivered a therapeutic shockfor a given set of electric cardiac signals monitored via the implantedelectrodes. The external computer device may analyze the received dataand transmit programming data to the IMD to adjust its therapy. Forexample, the programming data may indicate to the IMD to reduce theintensity of the therapeutic shock delivered to the patient.

[0015] Typically, the wireless transceiver within the IMD requiresrelatively high current pulses, thus resulting in a higher drain fromthe power source within the IMD. As the sophistication of the IMD andthe number of communication transmissions performed by the IMD isexpected to increase over the next several years, a much higher burdenmay be placed on the IMD's power source, thus reducing its life. Becausethe accessibility of the power source is achieved typically via asurgical procedure, this reduction in battery life is a concern.

[0016] The present invention is directed to reducing the effects of oneor more of the problems set forth above.

SUMMARY OF THE INVENTION

[0017] According to the present invention, an apparatus includes acontrol circuit coupled to a first power source to control the operationof the apparatus, the control circuit being adapted to receive powerfrom the first power source. A communication circuit is coupled to asecond power supply to communicate with an external device, thecommunication circuit being adapted to receive power from the secondpower source.

[0018] According to the present invention, an implantable medical deviceincludes a control circuit to control the operation of implantable themedical device and to obtain physiological data from a patient in whichthe implantable medical device is implanted. A communication circuit iscoupled to the control circuit to transmit the physiological data to anexternal device, a first power source is coupled to the control circuitto provide power to the control circuit, and a second power source iscoupled to the communication circuit to provide power to thecommunication circuit.

[0019] According to the present invention, a method for incorporating apower source in an implantable medical device includes providing powerto a control circuit by a first power source, the control circuitobtaining physiological data of a patient in which at least the controlcircuit is implanted; providing power to a communication circuit by asecond power source; and transmitting the physiological data from thecommunication circuit to an external device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a simplified schematic view of one embodiment of animplantable medical device (IMD) incorporating a power source inaccordance with the present invention;

[0021]FIG. 2 is a simplified schematic circuit diagram of a power sourcein accordance with the present invention for use with the IMD of FIG. 1;

[0022]FIG. 3 is a simplified schematic diagram of a first embodimentpower source in accordance with the present invention;

[0023]FIG. 4 is a simplified schematic diagram of a second embodimentpower source in accordance with the present invention;

[0024]FIG. 5A is a cross-sectional view of a third alternativeembodiment power source in accordance with the present invention;

[0025]FIG. 5B is a cross-sectional view of a variation of the embodimentof FIG. 5A;

[0026]FIG. 5C is a perspective view of the power source of FIG. 5Aincluding an internal, parallel connection;

[0027]FIG. 6 is a top view of a fourth embodiment power source inaccordance with the present invention;

[0028]FIG. 7 is a cross-sectional view of an IMD incorporating a fifthembodiment power source;

[0029]FIG. 8 is a simplified schematic diagram of a sixth embodimentpower source;

[0030]FIG. 9 is a graph showing a discharge curve for a conventionallybalanced battery;

[0031]FIG. 10 is a graph showing a discharge curve for an anode limitedbattery for use with the power source of FIG. 8;

[0032]FIG. 11 is a simplified block diagram of an implantable medicaldevice (IMD) incorporating a power source in accordance with anotherembodiment of the present invention;

[0033]FIG. 11A is a more detailed representation of a control circuit ofthe IMD of FIG. 11;

[0034]FIG. 12 illustrates the communication capabilities of the IMD ofFIG. 11 with an external data processing device;

[0035]FIG. 13 is a more detailed representation of the power source ofthe IMD of FIG. 11 in accordance with one embodiment of the presentinvention; and

[0036]FIG. 14 illustrates another more detailed representation of thepower source of the IMD of FIG. 13 according to another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037]FIG. 1 is a simplified schematic view of one embodiment of animplantable medical device (“IMD”) 20 in accordance with the presentinvention and its relationship to a human heart 22. The IMD 20 is shownin FIG. 1 as preferably being a pacemaker/cardioverter/defibrillator(PCD), although the IMD may alternatively be a drug delivery device, aneurostimulator, or any other type of implantable device known in theart. The IMD includes a case or hermetic enclosure 23 and associatedelectrical leads 24, 26 and 28. As described in greater detail below,the enclosure case 23 contains various circuits and a power source. Theleads 24, 26 and 28 are coupled to the IMD 20 by means of a multi-portconnector block 30, which contains separate ports for each of the threeleads 24, 26, and 28 illustrated.

[0038] In one embodiment, lead 24 is coupled to a subcutaneous electrode40, which is intended to be mounted subcutaneously in the region of theleft chest. Alternatively, an active “can” may be employed such thatstimulation is provided between an implanted electrode and enclosurecase 23. In yet another embodiment, stimulation is provided between twoelectrodes carried on a single multipolar lead.

[0039] The lead 26 is a coronary sinus lead employing an elongated coilelectrode that is located in the coronary sinus and great vein region ofthe heart 22. The location of the electrode is illustrated in brokenline format at 42, and extends around the heart 22 from a point withinthe opening of the coronary sinus to a point in the vicinity of the leftatrial appendage.

[0040] Lead 28 is provided with an elongated electrode coil 38 which islocated in the right ventricle of the heart 22. The lead 28 alsoincludes a helical stimulation electrode 44 which takes the form of anextendable/retractable helical coil which is screwed into the myocardialtissue of the right ventricle. The lead 28 may also include one or moreadditional electrodes for near and far field electrogram sensing.

[0041] In the system illustrated, cardiac pacing pulses are deliveredbetween the helical electrode 44 and the coil electrode 38. Theelectrodes 38 and 44 are also employed to sense electrical signalsindicative of ventricular contractions. Additionally,cardioverters/defibrillation shocks may be delivered between coilelectrode 38 and the electrode 40, and between coil electrode 38 andelectrode 42. During sequential pulse defibrillation, it is envisionedthat pulses would be delivered sequentially between subcutaneouselectrode 40 and coil electrode 38, and between the coronary sinuselectrode 42 and coil electrode 38. Single pulse, two electrodedefibrillation pulse regimens may also be provided, typically betweencoil electrode 38 and the coronary sinus electrode 42. Alternatively,single pulses may be delivered between electrodes 38 and 40. Theparticular interconnection of the electrodes to the IMD 20 will dependsomewhat on the specific single electrode pair defibrillation pulseregimen is believed more likely to be employed.

[0042] Regardless of the exact configuration and operation of the IMD20, the IMD 20 includes several basic components, illustrated in blockform in FIG. 2. The IMD 20 includes a high-power output circuit 50, alow-power control circuit 52, a power source 54 (shown with dashedlines) and circuitry 56. As described in greater detail below, the powersource 54 is preferably a dual-cell configuration, and can assume a widevariety of forms. Similarly, the circuitry 56 can include analog and/ordigital circuits, can assume a variety of configurations, andelectrically connects the power source 54 to the high power circuit 50and the low-power circuit 52.

[0043] The high-power output circuit 50 and the low-power controlcircuit 52 are typically provided as part of an electronics moduleassociated with the IMD 20. In general terms, the high-power outputcircuit 50 is configured to deliver an electrical pulse therapy, such asa defibrillation or a cardioversion/defibrillation pulse. In sum, thehigh-power output circuit 50 is responsible for applying stimulatingpulse energy between the various electrodes 38-44 (FIG. 1) of the IMD20. As is known in the art, the high-power output circuit 50 may beassociated with a capacitor bank (not shown) for generating anappropriate output energy, for example in the range of 0.1-40 Joules.

[0044] The low-power control circuit 52 is similarly well known in theart. In general terms, the low-power control circuit 52 monitors heartactivity and signals activation of the high-power output circuit 50 fordelivery of an appropriate stimulation therapy. Further, as known in theart, the low-power control circuit 52 may generate a preferred series ofpulses from the high-power output circuit 50 as part of an overalltherapy.

[0045] The power source 54 and associated circuitry 56 can assume a widevariety of configurations, as described in the various embodimentsbelow. Preferably, however, the power source 54 includes a first,high-rate cell 60 and a second, lower-rate cell 62, such as a medium- orlow-rate cell. Notably the first and second cells 60, 62 can be formedseparate from one another or contained within a singular enclosure.Depending upon the particular application, the high-rate cell 60 isconfigured to provide a stimulation energy of as little as 0.1 Joulesfor pacemakers to as much as 40 Joules for implantable defibrillators.As described below with reference to specific embodiments, the high-ratecell 60 can assume a wide variety of forms as is known in the art.Preferably, the high-rate cell 60 includes an anode, a cathode and anelectrolyte. The anode is preferably formed to include lithium, eitherin metallic form or ion form for re-chargeable applications. With thisin mind, the high-rate cell 60 is most preferably a spirally-woundbattery of the type disclosed, for example, in U.S. Pat. No. 5,439,760to Howard et al. for “High Reliability Electrochemical Cell andElectrode Assembly Therefor” and U.S. Pat. No. 5,434,017 to Berkowitz etal. for “High Reliability Electrochemical Cell and Assembly Therefor,”the disclosures of which are hereby incorporated by reference. Thehigh-rate cell 60 may less preferably be a battery having aspirally-wound, stacked plate or serpentine electrodes of the typedisclosed, for example, in U.S. Pat. Nos. 5,312,458 and 5,250,373 toMuffuletto et al. for “Internal Electrode and Assembly Method forElectrochemical Cells;” U.S. Pat. No. 5,549,717 to Takeuchi et al. for“Method of Making Prismatic Cell;” U.S. Pat. No. 4,964,877 to Kiester etal. for “Non-aqueous Lithium Battery;” U.S. Pat. No. 5,14,737 to Post etal. for “Electrochemical Cell With Improved Efficiency SerpentineElectrode;” and U.S. Pat. No. 5,468,569 to Pyszczek et al. for “Use ofStandard Uniform Electrode Components in Cells of Either High or LowSurface Area Design,” the disclosures of which are herein incorporatedby reference. Alternatively, the high-rate cell 60 can include a singlecathode electrode.

[0046] Materials for the cathode of the high-rate cell 60 are mostpreferably solid and comprise as active components thereof metal oxidessuch as vanadium oxide, silver vanadium oxide (SVO) or manganesedioxide, as is known in the art. Alternatively, the cathode for thehigh-rate cell 60 may also comprise carbon monoflouride and hybridsthereof or any other active electrolytic components and combination.Where SVO is employed for the cathode, the SVO is most preferably of thetype known as “combination silver vanadium oxide” (or “CSVO”) asdisclosed in U.S. Pat. Nos. 5,221,453; 5,439,760; and 5,306,581 toCrespi et al, although other types of SVO may be employed.

[0047] It is to be understood that electrochemical systems other thanthose set forth explicitly above may also be utilized for the high-ratecell 60, including, but not limited to, anode/cathode systems such aslithium/silver oxide; lithium/manganese oxide; lithium/V₂O₅;lithium/copper silver vanadium oxide; lithium/copper oxide; lithium/leadoxide; lithium/carbon monoflouride; lithium/chromium oxide;lithium/bismuth-containing oxide; lithium/copper sulfate; mixtures ofvarious cathode materials listed above such as a mixture of silvervanadium oxide and carbon monoflouride; and lithium ion rechargeablebatteries, to name but a few.

[0048] In general terms, the second, lower-rate cell 62 has a ratecapability that is less than that of the high-rate cell 60, and issufficient to power the low-power control circuit 52. For example, inone preferred embodiment, the second, lower-rate cell 62 is a mediumrate, SVO cell, more preferably SVO/CF_(x) cell. Alternatively, thesecond, lower-rate cell 62 can be a low-rate, lithium/iodine pacemakerbattery having a current drain in the range of 10-30 microamps. As knownin the art, acceptable constructions of the second, lower-rate cell 62include, for example, a single cathode electrode design described inU.S. Pat. No. 5,716,729 to Sunderland et al. for “Electrochemical Cell,”the disclosure of which is incorporated by reference. As used throughoutthe specification, reference to a “lower-rate cell” includes both alow-rate cell and a medium-rate cell. Regardless of the exactconstruction, the high rate cell 60 and the lower-rate cell 62preferably have similar beginning of life (BOL) voltages (e.g., lessthan 100 mV). Further, it is preferred that the cells 60, 62 havesimilar depletion voltages so that the capacity of each of the cells 60,62 is efficiently used when the first of the cells 60 or 62 reachesdepletion.

[0049] With the above-described parameters of the high-rate cell 60 andthe second, lower-rate cell 62 in mind, one preferred combination A of apower source 54A and circuitry 56A is depicted schematically in FIG. 3.The power source 54A includes a first, high-rate cell 60A and a second,lower-rate cell 62A as described above. In addition, circuitry 56Aelectrically connects the high-rate cell 60A and the lower-rate cell 62Ain parallel to the high-power output circuit 50 and the low-powercontrol circuit 52. In particular, the circuitry 56A includes a switch70 configured to selectively uncouple the high-rate cell 60 from thelow-power control circuit 52. In this regard, the circuitry 56A caninclude additional components/connections (not shown) for activating anddeactivating the switch 70 in response to operational conditionsdescribed below.

[0050] The power source/circuitry configuration A provides a distinctadvantage over prior art, single-cell designs. For example, duringoperation of the IMD 20 (FIG. 1), the power source 54A is, fromtime-to-time, required to deliver a high-current pulse or charge to thehigh-power output circuit 50 while maintaining a voltage high enough tocontinuously power the low-power control circuit 52. If the supplyvoltage drops below a certain value, the IMD 20 will cease operation.The power source/circuitry configuration A places the high-rate cell 60Aand the lower-rate cell 62A in parallel to power the low-power controlcircuit 52 during periods when the high-power output circuit 50 is notactivated. During a transient high power pulse, such as a defibrillationpulse, the switch 70 is opened to uncouple the high-rate cell 60A fromthe low-power control circuit 52. The lower-rate cell 62A remainselectrically connected to the low-power control circuit 52. Thus, thelower-rate cell 62A continuously powers the low-power control circuit52, regardless of any voltage drop experienced by the high-rate cell60A. With the parallel configuration of the circuitry 56A, the high-ratecell 60A and the lower-rate cell 62A can be operated in combination forapproximately the entire useful life of the respective cells 60A, 62A.Further, where desired, the cells 60A and/or 62A can be sized and shapedto satisfy certain volumetric or shape constraints presented by the IMD20 (FIG. 1).

[0051] An alternative embodiment power source/circuitry configuration Bis depicted schematically in FIG. 4. The power source/circuitryconfiguration B includes a power source 54B and circuitry 56B. The powersource 54B includes a first, high-rate cell 60B and a second, lower-ratecell 62B. The circuitry 56B connects the high-rate cell 60B and thelower-rate cell 62B in parallel with the high-power output circuit 50and the low-power control circuit 52, and includes a switch 80. Theswitch 80 is configured to selectively uncouple the high-rate cell 60Bfrom the low-power control circuit 52, such that the circuitry 56B caninclude additional components/connections (not shown) for activating anddeactivating the switch 80 in response to operational conditionsdescribed below.

[0052] The power source 54B is preferably a reservoir battery wherebyboth the high-rate cell 60B and the lower-rate cell 62B are maintainedwithin a single case, shown generally at 82. In this regard, thehigh-rate cell 60B includes an anode/cathode combination that iselectrochemically correlated (preferably identical) with ananode/cathode construction of the lower-rate cell 62B such that a commonelectrolyte 84 activates both cells 60B, 62B. For example, the high-ratecell 60B can be a high-rate Li/SVO, whereas the lower-rate cell 62B is ahigh-volumetric efficiency cell such as Li/SVO or a Li/MnO₂ cell with apellet design. Alternatively, other constructions for the cells 60B,62B, as previously described, are equally acceptable.

[0053] Connecting the cells 60B, 62B in parallel, via the circuitry 56B,to the high-power output circuit 50 and the low-power control circuit 52allows for both cells 60B, 62B to power the low-power control circuit52, thereby extending the useful life of the power source 54B. Further,as with the power source/circuitry configuration A (FIG. 3) previouslydescribed, the switch 80 ensures low-power control circuit 52 operationduring transient high power pulses by the high-power output circuit 50.For example, when the high power output circuit 50 is prompted todeliver a high power pulse or charge, the circuitry 56B opens the switch80 to uncouple the high-rate cell 60B from the low-power control circuit52. The lower-rate cell 62B remains electrically connected, providingcontinuous, uninterrupted power to the low-power control circuit 52.

[0054] In addition, the lower-rate cell 62B can serve to recharge thehigh-rate cell 60B. More particularly, after the high-rate cell 60B ispulsed, the potential of the high-rate cell 60B will be lower than thatof the lower-rate cell 62B. When the lower-rate cell 62B is re-connectedto the high-rate cell 60B (via the switch 80), the lower-rate cell 62Bwill be discharged and the high-rate cell 60B correspondingly chargeduntil they reach equal potentials. Electrons move from the anode of thelower-rate cell 62B to the anode of the high-rate cell 60B, and from thecathode of the high-rate cell 60B to the cathode of the lower-rate cell62B. In one preferred embodiment, for recharging to occur, the high-ratecell 60B must possess at least some degree of rechargeability. That isto say, the high-rate cell 60B may not be rechargeable per the abovedescription if discharged to a high degree. It has been found thatconfiguring the high-rate cell 60B to exhibit a “micro-rechargeability”characteristic allows the small amount of capacity removed duringoperation of the high-power output circuit 50 (e.g., a therapy) to bereplaced. It has further been found that a high-rate cell 60B includingan SVO cathode exhibits this desired micro-rechargeabilitycharacteristic. Alternatively, other cathode materials may also beacceptable. Notably, this same recharging mechanism applies to theconfiguration A (FIG. 3) previously described.

[0055] As an additional advantage, the high-rate cell 60B can be sized(e.g., cell volume) to satisfy the requirements of the high-power outputcircuit 50, without specific concern for powering the low-power controlcircuit 52. As previously described, with prior art, single celldesigns, cell volume is highly inefficient. The power source 54Bovercomes this problem by minimizing the size of the high-rate cell 60B,and utilizing a more conveniently sized lower-rate cell 62B. In otherwords, the high-rate cell 60B can be a relatively simple shape that isconducive to coiled, serpentine, or other high-electrode areaconstruction (but possibly with a lower volumetric energy density),whereas the lower-rate cell 62B can be of a shape that conforms andefficiently utilizes a desired volumetric shape of the IMD 20, such as a“D”-shaped pellet or bobbin cell with a relatively high volumetricenergy density. The resulting power source 54B, by virtue of its unique,complex shape, utilizes the volume available in the IMD 20 and thuscontributes to the IMD 20 having an optimal volume.

[0056] Yet another alternative embodiment power source/circuitryconfiguration C is depicted in cross-section in FIG. 5A. Moreparticularly, FIG. 5A shows a power source 54C including a high-ratecell 60C, a reservoir pellet 90, and a lithium body 92 that serve as alower-rate cell 62C. The high-rate cell 60C, the pellet 90, and thelithium body 92 are disposed within a case 94 further containing anelectrolyte 96. Although not shown in FIG. 5A, the high-rate cell 60Cand the lower-rate cell 62C (comprised of the reservoir cathode pellet90 and the lithium body 92) are connected in parallel to the high-poweroutput circuit 50 (FIG. 2) and the low-power control circuit 52 (FIG. 2)by circuitry (not shown) that may or may not include a switch. Further,the lithium body 92 is approximately the same length and width as thecathode reservoir pellet 90.

[0057] The high-rate cell 60C can assume a number of constructions, butpreferably includes a coiled anode 98 and cathode 100. For example, theanode 98 is preferably a lithium material, whereas the cathode 100 is anappropriate metal-containing material (e.g., a metal oxide or metalsulfide), preferably SVO. Regardless, the anode 98 and the cathode 100are preferably wound about the reservoir pellet 90. Alternatively, thereservoir pellet 90 and the lithium body 92 can be positioned outside ofthe winding of the high-rate cell 60C, as shown, for example, by thealternative embodiment of FIG. 5B.

[0058] Returning to FIG. 5A, the reservoir pellet 90 is of the samecomposition as the cathode 100. For example, in a preferred embodiment,the reservoir pellet 90 is a dense SVO or MnO₂ cathode pellet.Similarly, the lithium body 92 is of the same composition as the anode98, and serves to balance the capability of the reservoir pellet 90. Inthis regard, the lithium body 92 need not be a separate element, butinstead, an inner-most turn 102 of the anode 98 (i.e., surrounding thereservoir pellet 90) can be thickened (i.e., provided with additionallithium material).

[0059] The power source/circuitry configuration C provides the powersource 54C with a higher energy density than a conventional parallelplate or coil configuration by utilizing the reservoir pellet 90 tocharge the high-rate cell 60C without the difficulties of fabricating,coiling, or folding multiple thick electrodes.

[0060] During use, the high-rate cell 60C and the reservoir pellet 90operate in parallel to power the low power control circuit 52 (FIG. 2).During a transient high-pulse operation, the high-rate cell 60C and thereservoir pellet 90 operate to power the high-power output circuit 50(FIG. 2). Most of the power is delivered by the high-rate cell 60C dueto its low internal resistance as compared to the lower-rate cell 62C(again, defined by the reservoir cathode pellet 90 and the lithium body92). Following transient high-pulse operation, the lower-rate cell 62Cpreferably acts to recharge the high-rate cell 60C as previouslydescribed with respect to the power source 54B (FIG. 4). In particular,the reservoir pellet 90 serves as an auxiliary cathode, acceptingelectrons and lithium ions from the cathode 100 following the transienthigh-pulse operation. For example, where the reservoir pellet 90 iscomprised of a material that is chemically compatible with thecomposition of the cathode 100 (e.g., SVO or MnO₂), as the high-ratecell 60C is discharged, the cathode 100 is charged or oxidized by theflow of electrons and lithium ions between the cathode 100 and thereservoir pellet 90. The resulting power source 54C has a higher averagevoltage, a higher volumetric energy density and an improved end of lifevoltage signal than a similar cell without the reservoir pellet 90.Further, the lithium body 92 balances the capacity of the reservoirpellet 90, thereby promoting recharging of the high-rate cell 60Cfollowing a transient high power pulse.

[0061] In one more preferred embodiment of the power source 54C, thehigh-rate cell 60C and the lower-rate cell 62C (or the reservoir pellet90) are connected in parallel, internal to the power source 54C itself.For example, FIG. 5C illustrates one interconnection techniqueassociated with the configuration C of FIG. 5A. As a point of reference,a portion of the case 94 has been removed to better illustrate componentinterconnection. With this in mind, the power source 54C furtherincludes a first conductive tab 102, a second conductive tab 104, and aconnector 106. The first tab 102 is connected to and extends from thecathode 100 associated with the high-rate cell 60C. Conversely, thesecond tab 104 is connected to and extends from the reservoir (orcathode) pellet 90 forming the lower-rate cell 62C. Finally, theconnector 106 interconnects the tabs 102, 104, and terminates in a feedthrough pin 108 otherwise extending outwardly from the battery case 94.

[0062] By internally connecting the cells 60C and 62C in parallel, onlya single one of the feedthroughs 108 is required, thereby reducing thecosts and complexities of other dual batter designs in which two or morefeedthroughs are required. It will be understood that the constructionof FIG. 5C necessitates that the cells 60C, 62C are not independentlydischargeable, and a switch, such as the switch 80 of FIG. 4 is notavailable. However, the design promotes shape flexibility and volumetricefficiency. For example, one particular manufacturing concern associatedwith high-energy IMD power supplies is the requirement, due to knownsafety concerns, of a wound cell utilizing a thick cathode. Where awound design is employed, the thick cathode material tends to crack inthe corners and transmits stress through other components (such as aseparator plate and/or lithium anodes). This may, in turn, lead tointernal shorts. With the configuration of FIG. 5C, however, asubstantial fraction of the energy supply is stored in the reservoirpellet 90 (or lower rate cell 62C), and the adjacent lithium body 92.The pellet 90 is not wound, and thus can be relatively thick withoutpresenting the stress concerns associated with a wound cathode material.Because a substantial fraction of the energy is stored in the pellet 90,the cathode 100 material associated with the high-rate cell 60C can nowbe relatively thin, and thus more readily wound without experiencingstress-related defects. Further, by forming the reservoir pellet 90 tobe relatively thick, a radius of the inner most winding associated withthe high rate cell 60C is increased or greater than that found withconventional wound cells, again reducing winding-caused stress.

[0063] Yet another alternative power source/circuitry configuration Dhaving enhanced volumetric efficiency is depicted schematically in FIG.6. The configuration D includes a power source 54D and circuitry 56D.The power source 54D includes a case 110 maintaining a high-rate cell60D, a lower-rate cell 62D, and an electrolyte (not shown). Thecircuitry 56D connects the cells 60D, 62D in parallel with thehigh-power output circuit 50 (FIG. 2) and the low-power control circuit52 (FIG. 2). Although illustrated schematically in FIG. 6, the high-ratecell 60D can assume any of the forms previously described and ispreferably of a simple shape such that is conducive to assuming acoiled, serpentine, or other high-surface area electrode configuration.Conversely, the lower-rate cell 62D is a relatively low-surface areaauxiliary electrode assuming an irregular shape, such as a D-shape,otherwise conforming and efficiently utilizing an available volume ofthe case 110. Once again, the lower-rate cell 62D can be comprised ofany of the material(s) previously described, and can be a medium- orlow-rate cell. Regardless, the resulting power source 54D, by virtue ofits unique, complex shape, utilizes the volume available in the IMD 20(FIG. 1) and thus contributes to an optimally sized device.

[0064] In operation, the power source 54D operates similar to previousembodiments, with the high-rate cell 60D and the lower-rate cell 62Doperating in parallel to power the high-power output circuit 50 (FIG. 2)and the low-power control circuit 52 (FIG. 2). In this regard, thecircuitry 56D associated with the power source 54D may include a switch(not shown) that uncouples the high-rate cell 60D from the low-powercontrol circuit 52 during transient high power pulses. Operation of thelower-rate cell 62D in isolation from the high-rate cell 60D willcontinuously power the low-power control circuit 52 without concern forthe voltage drop associated with the high-rate cell 60D. Further, whenthe power source 54D is subjected to a high-current pulse discharge, thehigh-rate cell 60D and the lower-rate cell 62D will equilibrate betweenpulses and thus stay at the same depth of discharge, with most of thecapacity of the high-rate cell 60D being discharged at a higher voltagethan would be observed without the lower-rate cell 62D connected inparallel.

[0065] Yet another, related alternative power source/circuitryconfiguration E having enhanced volumetric efficiency is depicted aspart of an IMD 112 in FIG. 7. More particularly, the IMD 112 is shown asincluding a case 114, a circuit 116 (shown generally in FIG. 7), and thepower source 54E. The power source 54E includes a high-rate cell 60E anda lower rate cell 62E. With the embodiment of FIG. 7, the cells 60E, 62Eare separately formed (i.e., separate enclosures) and are connected inparallel via circuitry 56E. Notably, the circuitry 56E does not includea switch, and the cells 60E, 62E are not independently dischargeable.

[0066] Though illustrated schematically in FIG. 7, the high-rate ratecell 60E can assume any of the forms previously described and ispreferably of a simple shape, conducive to assuming a coiled,serpentine, or other high-surface area electrode configuration.Conversely, the lower-rate cell 62E is a relatively low-surface areaauxiliary electrode shaped to efficiently utilize an available volume ofthe case 114. In one preferred embodiment, the high-rate cell 60E is athin film battery known in the art. In this regard, one preferred methodof manufacturing a thin electrode is to prepare a slurry of electrodematerial in an appropriate solvent. This slurry is then applied to athin foil substrate as the current collector. To this end, the mostcommon method is to use a “knife over roller” approach, whereby theslurry is applied to a moving web (e.g., the metal foil) using a knifeedge to control thickness (i.e., a Doctor blade). The solvent is thenevaporated leaving a thin film of cathode material. Alternatively, otherknown thin electrode manufacturing techniques are equally acceptable.

[0067] By forming the high rate cell 60E as a thin film battery, thepower source 54E is characterized by an improved volumetric efficiency.Further, especially where the IMD 112 is an ICD, the power source 54Epresents improved scaleability. As a point of reference, ICD batteriesare typically built with maximum safe power capability (i.e., maximumsafe electrode surface area). Thus, changing the size of a “standard”ICD battery in one dimension while maintaining a specific surface areatypically imposes more geometric constraints than can be satisfied. As aresult, for differently sized ICD applications, the “standard” ICDbattery must often be changed in two dimensions, and therefore is notscaleable. The dual cell design of FIG. 7 overcomes this problem. Inparticular, by forming the high-rate cell 60E as a thin electrode allowsthe high-rate cell 60E to be located underneath the circuit 116.Conversely, the lower rate cell (preferably a medium-rate cell) 62E isconstructed to have the same thickness as the internal dimensions of thecase 114 (i.e., the same thickness as the circuits 116 and the high-ratecell 60E). As shown in FIG. 7, then, the lower rate cell 62E ispositioned adjacent the circuit 116/high-rate cell 60E stack. Thehigh-energy capacitors (not shown) of the ICD 112 are located on theother side of the lower-rate cell 62E and match the medium rate cell 62Ein thickness. For a differently sized ICD, the lower rate cells 62E canbe scaled in one dimension to provide the energy needs for a particularapplication. However, the circuit 116, the high-rate cell 60E, thecapacitors, and any device connector blocks (not shown) are all fixedcomponents that do not vary. Thus, the configuration of FIG. 7 meetsdesired scaleability criteria.

[0068] Another alternative embodiment power source/circuitryconfiguration F is depicted schematically in FIG. 8. The configuration Fincludes a power source 54F and associated circuitry 56F. Once again,the power source 54F includes a first, high-rate cell 60F and a second,lower-rate cell 62F. The circuitry 56F connects the high-rate cell 60Fand the lower-rate cell 62F to the high-power output circuit 50 and thelow-power control circuit 52. Unlike previous embodiments, the circuitry56F need not necessarily connect the cells 60F, 62F in parallel.Further, while the lower-rate cell 62F is highly similar to previouslydescribed embodiments, the high-rate cell 60F is preferably an anodelimited cell as described below.

[0069] In particular, for the configuration F, the high-rate cell 60Fincludes a solid cathode, liquid organic electrolyte and a lithium anodefor delivering high current pulses. The cell 60F further includes acasing (not shown) containing the cell components and the cathodestructure generally wound in a plurality of turns, with the lithiumanode interposed between the turns of the cathode winding. The casingalso contains a non-aqueous liquid organic electrolyte preferablycomprising a combination of lithium salt and an organic solventoperatively contacting the anode and the cathode. An electricalconnection is provided to the anode and an electrical connection isprovided to the cathode. The cathode includes an active material such asSVO or MnO₂.

[0070] With the above-construction, the high-rate cell 60F is avolumetrically constrained system. The amounts of each component thatgoes into the cell 60F (cathode, anode, separator, current collectors,electrolytes, etc.) cannot exceed the available volume of the batterycase. In addition, the appropriate amount of some components dependsupon the amount of other components that are used. These components mustbe “balanced” to provide discharge to the extent desired.

[0071] For example, in a cathode limited Li/SVO battery such as is usedin a defibrillator application, the capacity (Q₊) of the cathode mustnot exceed the capacity (Q⁻) of the anode. The volume occupied by theother battery components also depends on the cathode capacity (Q₊) asreflected by the amount of cathode material in the battery. All of thebattery components must be adjusted for a given battery volume.

[0072] Conventionally balanced lithium anode cells used with ICDs arebalanced with sufficient lithium and electrolyte to discharge thecathode to completion. However, conventionally balanced cells haveimpedances that increase with time and depth-of-discharge. The powercapability of these cells is limited by electrode area constraintsimposed for safety reasons. Historically, it has been possible to usenearly the total capacity of the battery while maintaining adequatepower (i.e., acceptable charge times). However, over time,conventionally balanced high-rate cells exhibit increased charge timesdue to increased cell impedance. When the cell can no longer satisfycharge time requirements, the ICD (or other IMD) must be replaced. Tothis end, industry standards have implemented more rigorous charge timerequirements. Hence, it has become increasingly difficult to use theentire cell capacity before charge time failure.

[0073] One example of the above-described concern experienced by aLi/SVO type cell is illustrated graphically in FIG. 9. In particular, aconventional, Li/SVO high-rate cell design experiences a decrease involtage over time as shown by curve 120. In addition, due to theincrease in internal resistance over time results in an increasingcapacitor charge time, as represented by the curve 122. As a point ofreference, the curves 120, 122 extend from a beginning of life (BOL)point to an end of life (EOL) point. Just prior to EOL, manufacturerstypically delineate a potential loss of function (indicated at “PLF” inFIG. 9) for the power source with respect to a particular IMDapplication. PLF is determined by circuit performance requirements ofthe IMD. For the example of FIG. 9, according to manufacturer standards,the conventionally balanced cell will experience a potential loss offunction (PLF) at approximately 2.20 volts. To ensure that the IMD isexplanted and replaced prior to PLF, industry standards require the IMDto provide an elective replacement indicator (ERI) to the user. The ERIis normally designated by the manufacturer with reference to the voltagecurve 120 just prior to the PLF. For example, a manufacturer's standardsmay require that the IMD continue to operate for three months after ERI.With this standard in mind, the manufacturer works backwards from thePLF to select an ERI value that satisfies the so-selected standard. Withreference to the example of FIG. 9, a common ERI value is 2.45 volts.

[0074] With the above definitions in mind, FIG. 9 illustratesgraphically that the charge time curve 122 is dependent upondepth-of-discharge or time, increasing from BOL to both ERI and PLF. Dueto this time dependence, and as a point of reference, the charge timefor a typical high-rate cell useful with an IMD is approximately 8seconds at BOL, 14 seconds at ERI, and 25 seconds at PLF. As IMDperformance requirements continue to evolve, it is highly likely thatcharge times in excess of 16 seconds may no longer be acceptable. Inother words, future industry requirements may require a PLF value of 16seconds (and thus a correspondingly decreased ERI value). While an IMDincorporating a lithium-based high-rate cell can be programmed toprovide an earlier ERI signal (relative to the charge time curve 120),due to the dependence upon depth-of-discharge or time, only a smallportion of the battery's capacity will be used at this reduced ERIlevel. For example, at ERI corresponding with a charge time of 12seconds, approximately 40% of a conventional cell's capacity has beenused. Obviously this low efficiency is highly undesirable.

[0075] To overcome the time-dependent characteristics associated withprevious lithium-based high-rate cells, the power source 54F (FIG. 8)forms the high-rate cell 60F (FIG. 8) to be anode limited. Inparticular, the high-rate cell 60F is preferably a lithium limited cellas described, for example, in U.S. Pat. No. 5,458,997, the teachings ofwhich are incorporated herein by reference. Generally speaking,available lithium-based high-rate cells, such as Li/SVO, Li/MnO₂, etc.,are re-balanced such that the cell contains sufficient lithium andelectrolyte to be discharged only to a first voltage plateau (labeled as124 in FIG. 9). The volume made available by using less lithium andelectrolyte allows more room for cathode material, thereby extending thefirst voltage plateau as shown by the dotted line 126. With thisconfiguration, the lithium anode is depleted prior to cathode depletion,thereby prohibiting the formation of gas. In addition, the lithiumlimited design generates minimal impedance over a majority of thebattery's life. In one preferred embodiment, the lithium limited,high-rate cell 60F is a SVO/CF_(x) hybrid cathode design, where x is inthe range of 0.9-1.1.

[0076] As illustrated graphically in FIG. 10, the lithium limitedhigh-rate cell 60F (FIG. 8) exhibits charge time characteristics thathave little dependence upon depth-of-discharge or time. As a point ofreference, FIG. 10 depicts a voltage curve 130 and a charge time curve132. As compared to the conventionally balanced cell performancecharacteristics illustrated in FIG. 9, the voltage curve 130 of thelithium limited high-rate cell 60F has an extended first voltage plateau134, and a rapid voltage decrease after the second voltage plateau 136.Importantly, however, prior to a second voltage plateau 136, the chargetime curve 132 increases only slightly, if at all, with increaseddepth-of-discharge and/or time. Effectively, then, the lithium limitedhigh-rate cell 60E is characterized by a rate capability that exhibitsminimal dependence on time or depth-of-discharge throughout a majorityof the battery's life. With this characteristic in mind, an IMDincorporating the power source 54F (FIG. 8) including the high-rate cell60F can be programmed to establish the PLF and ERI values shown in FIG.10.

[0077] By way of example, and in accordance with one preferredembodiment, the PLF is established at approximately 2.6 volts and theERI at 2.65 volts. At these values, the rate capability or charge timecurve 132 exhibits minimal dependence upon depth-of-discharge and time.For example, the BOL charge time is approximately 8 seconds, the ERIcharge time is approximately 10 seconds, and the PLF charge time isapproximately 16 seconds. Following the second voltage plateau 136, thecharge time rapidly increases to EOL. However, unlike conventionallybalanced cells, the ERI and PLF of the anode limited high-rate cell 60Fare relatively close to the EOL (relative to an overall length of thevoltage curve 130). Thus, unlike conventionally balanced high-ratecells, the anode limited high-rate cell 60F allows for selection of anERI value at which rate capability and charge time has minimaldependence upon depth-of-discharge or time, and results in a largeportion of the cell's 60F capability being utilized. More particularly,the ERI of the high-rate cell 60F is selected such that at least 40percent of the cathode is consumed; preferably at least 50 percent; morepreferably at least 60 percent; most preferably at least 75 percent.

[0078] As previously described, with embodiment F (FIG. 8), thehigh-rate cell 60F and the lower-rate cell 62F need not necessarily beconnected in parallel. However, with parallel wiring, the lower-ratecell 62F will effectively recharge the high-rate cell 60F following atransient high power pulse, according to the recharging mechanismpreviously described. Further, with the parallel configuration, it ispreferred that the lower-rate cell 62F be designed to have a highervoltage (beyond BOL) than the high-rate cell 60F such that as the cells60F, 62F are discharged, the high-rate cell 62F will remain nearer itsBOL voltage and rate capability through more of the cell's 60F usefullife. In an even further preferred embodiment of configuration Femploying a parallel construction, the high-rate cell 60F is alithium-limited SVO cell and the lower-rate cell 62F is a SVO/CF_(x)hybrid cathode low-rate cell. This construction provides both of thecells with similar BOL voltages, similar depletion voltages (e.g.,greater than 90% depletion at PLF), and the lower-rate cell 62F willhave a higher voltage (beyond BOL) than the high-rate cell 60F.

[0079] The IMD with dual cell power source of the present inventionprovides a marked improvement over previous designs. In one embodiment,by connecting a first, high-rate cell and a second, lower-rate cell inparallel to a control circuit and an output circuit, and including aswitch to selectively uncouple the high-rate cell and the controlcircuit, the IMD will efficiently utilize the capacity in both cellsindependent of charge conditions. Regardless of whether the switch isincluded, the preferred parallel connection can facilitate thelower-rate cell recharging the high-rate cell following a transient highpower pulse depending upon a construction of the high-rate cell. Inanother alternative embodiment, the dual cells are provided as a singlereservoir. In yet another alternative embodiment, the high-rate cell hasan anode-limited construction and exhibits a charge time characteristicthat has minimal dependence on time or depth-of-discharge. With thisconfiguration, a majority of the high-rate cell's capacity is utilizedwhile satisfying rigorous charge time requirements.

[0080]FIG. 11 illustrates an implantable medical device (IMD) 200 inaccordance with another embodiment of the present invention. The IMD 200according to this embodiment may be provided in the form of a pacemaker,cardioverter, defibrillator, neural stimulator, or drug administeringdevice. It will be appreciated, however, that the IMD 200 may take theform of various other implantable medical devices, and, thus, need notnecessarily be limited to the aforementioned examples. For purposes ofillustration, however, the IMD 200 will be described in theconfiguration of an implantable cardiac defibrillator (ICD).

[0081] According to the illustrated embodiment, the IMD 200 comprises acontrol circuit 205 that controls the overall operation of the IMD 200.The control circuit 205 may be configured to monitor physiological datavia one or more electrodes disposed within the patient's body, which arecoupled to the IMD 200 via electrical leads. For example, the controlcircuit 205 may monitor cardiological activity via one or moreelectrodes implanted within the patient's heart. The control circuit 205may collect and process the physiological data received via theimplanted electrodes. Depending on the physiological data received atthe IMD 200 via the implanted electrodes, the control circuit 205 mayfurther be configured to deliver a therapy to a part of the patient'sbody. In accordance with the exemplary embodiment, the therapy may beprovided in the form of a therapeutic electric pulse that is deliveredto the patient's heart via the one or more electrodes implanted withinthe heart.

[0082] In accordance with one embodiment of the present invention, thecontrol circuit 205 is provided in the form of a processor unit 207, asshown in FIG. 11A, to control the overall operation thereof. In oneembodiment, the processor unit 207 may, for example, take the form of amicroprocessor, a microcontroller, or a digital signal processor. Thecontrol circuit 205 may further include a memory module 208 for storingthe physiological data that is received by the one or more electrodesimplanted within the patient's body. The memory module 208 may alsostore software firmware, and/or microcade that executes on the processorunit 207 for controlling the IMD 200.

[0083] Referring again to FIG. 11, the IMD 200 may further include ahigh power output circuit 210 for delivering an electrical pulsetherapy, such as a defibrillation or cardioversion/defibrillation pulsein accordance with the exemplary embodiment. The high power outputcircuit 210 may be provided in the form of a capacitor (not shown) forgenerating a high output electronic pulse that is delivered to thepatient's heart via the one or more electrodes that are implantedtherein. According to the illustrated embodiment, the high power outputcircuit 210 may receive a control signal from the control circuit 205 todeliver the high output electric shock in response to the analysis ofthe physiological data (i.e., electric cardiac signals) received via theone or more electrodes implanted within the patient's heart.

[0084] In accordance with the illustrated embodiment, the IMD 200 isfurther provided with a communication interface circuit 215, which mayprovide communication capabilities for the IMD 200 to communicate withan external data processing device. The data processing device may beconfigured to monitor and/or analyze the physiological data that iscollected and subsequently transmitted by the IMD 200. It will beappreciated, however, that the communication interface circuit 215 mayalso be configured to communicate with various other devices that areexternal to the patient's body without departing from the spirit andscope of the present invention. In an alternative embodiment, thecommunication interface circuit 215 may communicate with a transmittingdevice (not shown) that is external to the IMD 200, but within thepatient's body. This transmitting device may then communicate with anexternal data processing unit.

[0085] According to the illustrated embodiment, the communicationinterface circuit 215 is configured to communicate physiological dataobtained by the control circuit 205 from the one or more electrodesimplanted within the patient's body. The communication interface circuit215 may also be configured to receive data that is generated by anotherdevice externally from the IMD 200 that is to be processed by thecontrol circuit 205. According to the illustrated embodiment, thecommunication interface circuit 215 communicates data with the externaldevice via wireless communication.

[0086] In accordance with the illustrated embodiment, the IMD 200 isfurther configured with a power source 220 to provide electrical powerto the control circuit 205, high power output circuit 210 and thecommunication interface circuit 215. The power source 220 inherentlyplays a significant role in the operation of the IMD 200 since the IMDmay enter of limited function mode as the battery approachesend-of-life. As such, the IMD may not be capable of delivering anappropriate therapy to the patient, thereby compromising the patient'shealth. Moreover, because the IMD 200 is implanted within the patient'sbody, battery accessibility usually requires a surgical procedure.Accordingly, if the power source 220 fails, the patient's health may beplaced in jeopardy until such procedure is performed.

[0087] Turning now to FIG. 12, the communication capabilities of the IMD200 with an external device is shown in accordance with one embodimentof the present invention. The communication interface circuit 215 of theIMD 200 is configured with a wireless interface 230 for communicatingthrough a wireless communication medium 232 to a data processing device240 via a data transfer device 235. In accordance with the illustratedembodiment, the wireless interface 230 may take the form of a radiofrequency (RF) transceiver that transmits and receives radio frequencysignals with the data transfer device 235, which is also configured withan RF transceiver. It will be appreciated, however, that other forms ofcommunication protocols may be utilized between the wireless interface230 of the IMD 200 and the data transfer device 235 either in lieu of orin addition to radio frequency communication without departing from thespirit and scope of the present invention. For example, thecommunication protocol utilized between the wireless interface 230 andthe data transfer device 235 may include ultrasound communication, amongother types of communication.

[0088] According to the illustrated embodiment, the data transfer device235 may be provided in the form of a hand-held device that may beproximately placed to the implantable medical device 200 implantedwithin the patient's body. In this embodiment, the data transfer device235 is coupled to the data processing device 240 via a wired link 237.It will be appreciated, however, that the data transfer device 235 mayalternatively communicate with the data processing device 240 via awireless communication medium. For example, the wireless communicationmedium between the data transfer device 235 and the data processingdevice 240 may be an RF communication medium or an infrared (IR)communication medium. Alternatively, in one embodiment, data transferdevice 235 is eliminated, with the data transfer occurring directlybetween wireless interface 230 and data processing device 240.

[0089] It will further be appreciated that the power level of thecommunication signals between the communication interface circuit 215 ofthe IMD 200 and the data transfer device 235 may vary as well. Forexample, low power RF communication may be used between the IMD 200 andthe data transfer device 235 such that it may have to be placed withinclose proximity to the IMD 200. Alternatively, a higher transmissionpower level may be used over the RF communication medium 232 such thatclose physical proximity of the data transfer device 235 and the IMD 200is not necessary. Of course, it will be appreciated that the higher thetransmission power level that is used over the RF communication medium232, the higher the drain on the power source 220 of the IMD 200.

[0090] As previously mentioned, the physiological data is collected bythe control circuit 205 of the IMD 200 via the one or more implantedelectrodes within the patient's body. In one embodiment, thephysiological data may take the form of electrical cardiac signals fromelectrodes implanted within the patient's heart, and recorded within thememory module 208 of the IMD 200 in the form of an electrocardiogram,for example. The physiological data may subsequently be retrieved fromthe memory module 208 and transferred to the communication interfacecircuit 215 for wireless transmission to the data transfer device 235for monitoring and/or processing by the data processing device 240. Inan alternative embodiment, the physiological data may be obtained by thecontrol circuit 205 and transferred to the communication interfacecircuit 215 for transmission to the data transfer device 235 on areal-time basis as the data is sensed by the one or more implantedelectrodes within the patient's body. In addition to the transmission ofphysiological data to the data processing device 240 via the datatransfer device 235, the communication interface circuit 215 may alsotransmit data relating to the performance of the IMD 200. Theperformance data may include, for example, the effectiveness of apreviously delivered therapy from the IMD 200 to the patient's body.

[0091] In accordance with one embodiment of the present invention, thedata processing device 240 is provided in the form of a programmer orother computer. The data processing device 240 may be used to monitorand/or analyze the physiological data and/or performance datatransmitted from the IMD 200 via the communication interface circuit215. The data processing device 240 may also determine the efficiency ofthe therapy that is delivered by the IMD 200 based upon thephysiological data and performance data collected. For example, the dataprocessing device 240 may be used to determine whether the therapydelivered to the patient was of a proper energy intensity.

[0092] Based upon the analysis performed by the data processing device240 using the physiological and performance data that was received bythe IMD 200, the data processing device 240 may also be configured totransmit programming data to the IMD 200 via the data transfer device235 to adjust various settings of the IMD 200. For example, if it isdetermined by the data processing device 240 that the IMD 200 isdelivering a higher intensity of an electric pulse therapy signal thanis necessary (based upon the physiological data collected, for example),the programming data transmitted to the IMD 200 may reduce the intensityof the electric therapy signal delivered to the patient's body.

[0093] Typically, the communication interface circuit 215 of the IMD 200requires relatively high current pulses, thus resulting in a relativelyhigher drain from the power source 220. If a substantial amount of datais communicated between the communication interface circuit 215 and thedata transfer device 235, it may create a significant drain on the powersource 220 because of the high current pulses and the amount of time thecommunication interface circuit 215 is transmitting data. Additionally,as the amount of data communicated between the IMD 200 and the datatransfer device 235 increases, the burden placed on the power source 220is also increased, thereby decreasing the life of the power source 220within the IMD 200.

[0094] Turning now to FIG. 13, a more detailed representation of thepower source 220 is provided according to one embodiment of the presentinvention. The power source 220 comprises a primary power source 250 anda secondary power source 255. The primary power source 250 is used topower the control circuit 205 of the IMD 200, as well as the high-outputpower circuit 210. In accordance with one embodiment of the presentinvention, the primary power source 250 takes the form of alithium/CFx—CSVO battery. It will be appreciated, however, that theprimary power source 250 may take the form of various other batterytypes, which may include Li/CSVO, Li/CF_(x), Li/MnO₂, Li/l2, Li/SOCl₂,or other similar type chemistries.

[0095] In accordance with the illustrated embodiment, the secondarypower source 255 provides power to the communication interface circuit215 to alleviate any additional burden that the communication interfacecircuit 215 would have placed on the primary power source 250. Inaccordance with one embodiment, the secondary power source 255 isprovided in the form of a rechargeable battery. The secondary powersource 255 may comprise a lithium-ion battery with either a liquid orpolymer electrolyte. It will be appreciated, however, that the secondarypower source 255 may also take the form of other battery types, such asnickel/metal hydride or other similar type chemistries without departingfrom the spirit and scope of the present invention. According to theillustrated embodiment, the secondary power source 255 may be rechargedvia a transcutaneous magnetic induction process, as is well establishedin the art.

[0096] In accordance with one embodiment, the secondary power source 255powers only the communication interface circuit 215, thereby relievingthe burden of additional power requirements that the communicationinterface circuit 215 would require from the primary power source 250.Thus, in this embodiment, the secondary power source 255 is a dedicatedpower source for the communication interface circuit 215. Accordingly,the primary power source 250 needs to provide power only to theessential “life-support” operating circuitry of the control circuit 205and the high-output power circuit 210 without the need to provide powerto support the IMD 200's communication requirements (i.e., through thecommunication interface circuit 215), thereby conserving the power andlife of the primary power source 250. The primary power source may takethe form of any of the dual-cell embodiments discussed above.Alternatively, the primary power source may be a conventional,single-cell design.

[0097] In the illustrated embodiment of FIG. 13, the power sources 250and 255 may operate independently of each another. Thus, in oneembodiment, if one of the power sources 250, 255 fails, the other powersource 250, 255 continues to power its respective circuit(s).

[0098] Turning now to FIG. 14, the power source 220 is shown inaccordance with another embodiment of the present invention. In thisparticular embodiment, the primary power source 250 and the secondarypower source 255 are coupled to a power source switch 260, which iscapable of switching connections to provide power to the variouscomponents of the IMD 200. As mentioned with the configuration providedin FIG. 13, the primary power source 250 ordinarily provides power onlyto the control circuit 205 and the high output power circuit 210 of theIMD 200. The secondary power source 255, on the other hand, ordinarilyprovides power only to the communication interface circuit 215. Inaccordance with the illustrated embodiment of FIG. 14, the power sourceswitch 260 is configured to switch connections of the primary powersource 250 and/or the secondary power source 255 depending on whether ornot the power sources 250, 255 are depleted of their power.

[0099] In accordance with one embodiment, the switch 260 is coupled to apower level sensor 265, which is configured to determine the remainingpower level of the primary power source 250 and/or secondary powersource 255. The power level sensor 265 may be further configured todetermine whether the remaining power level of the primary and/orsecondary power sources 250, 255 has fallen below a predetermined powerlevel. Accordingly, the power source switch 260 may be configured toswitch connections between the circuits 205, 210, and 215 of the IMD 200and the primary and secondary power sources 250, 255 based upon thepower level being below the predetermined threshold value as determinedby the sensor 265. In one embodiment, the predetermined threshold valuemay be a power level just above a remaining power level of zero (i.e., adead battery).

[0100] For example, if the IMD 200 is transferring data between itscommunication interface circuit 215 and the data transfer device 235(FIG. 2), and the power level sensor 265 determines that the power levelof the secondary power source 255 is nearly depleted (i.e., below apredetermined threshold), the sensor 265 may send a control signal tothe switch 260 to couple the primary power source 250 to thecommunication interface circuit 215 of the IMD 200 so as not to disruptthe data transfer. Similarly, if the power level within the primarypower source 250 is determined to be depleted below a predeterminedthreshold, the power source switch 260 may switch the connections of thecontrol circuit 205 and/or high output power circuit 210 to receivepower from the secondary power source 255, as opposed to receiving powerfrom the primary power source 250.

[0101] In an alternative embodiment, the power source switch 260 mayinclude the circuitry to sense the power level remaining within theprimary power source 250 and/or the secondary power source 255, and toswitch connections between the circuits 205, 210, and 215 of the IMD 200and the primary and secondary power sources 250, 255 based upon thesensed power levels. That is, the sensor 265 for sensing the remainingpower level of the primary and secondary power sources 250, 255 may bean integral component of the power source switch 260 as opposed to beinga separate component as illustrated in FIG. 14.

[0102] Although the present invention has been described with referenceto preferred embodiments, it will be appreciated by those of ordinaryskill in the art that a wide variety of alternate and/or equivalentimplementations calculated to achieve the same purposes may besubstituted for the specific embodiments shown and described withoutdeparting from the spirit and scope of the present invention.

What is claimed is:
 1. An apparatus, comprising: first and second power sources; a control circuit coupled to the first power source to control the operation of the apparatus, the control circuit being adapted to receive power from the first power source; and a communication circuit coupled to the second power source to communicate with an external device, the communication circuit being adapted to receive power from the second power source.
 2. The apparatus of claim 1, wherein the first power source comprises a battery.
 3. The apparatus of claim 2, wherein the battery comprises at least one of a Li/CF_(x)—CSVO, Li/CSVO, Li/CF_(x), Li/MnO₂, Li/l2, and Li/SOCl₂ battery.
 4. The apparatus of claim 1, wherein the second power source comprises a rechargeable battery.
 5. The apparatus of claim 4, wherein the rechargeable battery comprises at least one of a lithium-ion and a nickel/metal-hydride battery.
 6. The apparatus of claim 1, further comprising: a switch for coupling the first power source to the communication circuit upon occurrence of a first predetermined event.
 7. The apparatus of claim 6, wherein the first and second power sources have a remaining power level associated therewith, the apparatus further comprising: a sensor for sensing the remaining power level of at least one of the first power source and second power source.
 8. The apparatus of claim 7, wherein the first predetermined event includes the sensor sensing the remaining power level of the second power source being below a remaining power level threshold.
 9. The apparatus of claim 7, wherein the switch includes means to couple the second power source to the control circuit upon occurrence of a second predetermined event.
 10. The apparatus of claim 9, wherein the second predetermined event includes the sensor sensing the remaining power level of the first power source being below a remaining power level threshold.
 11. The apparatus of claim 1, wherein the control circuit further is adapted to obtain physiological data of a patient in which the apparatus is implanted.
 12. The apparatus of claim 11, wherein the communication circuit includes means to transmit the physiological data to the external device.
 13. The apparatus of claim 11, wherein the communication circuit includes means to receive programmed instructions from the external device.
 14. The apparatus of claim 11, further comprising a high-power output circuit coupled to the central circuit to deliver a therapy to the patient depending on the physiological data obtained from the control circuit.
 15. The apparatus of claim 14, wherein the high-power output circuit receives power from the first power source.
 16. The apparatus of claim 15, wherein the first power source comprises a high-rate cell and a low-rate cell.
 17. The apparatus of claim 15, wherein the high-rate cell provides power to the high-power output circuit and the low-rate cell provides power to the control circuit.
 18. An implantable medical device, comprising: a control circuit to control the operation of the implantable medical device and to obtain physiological data from a patient in which the implantable medical device is implanted; a communication circuit coupled to the control circuit to transmit the physiological data to an external device; a first power source coupled to the control circuit to provide power to the control circuit; and a second power source coupled to the communication circuit to provide power to the communication circuit.
 19. The implantable medical device of claim 18, wherein the first power source comprises a battery.
 20. The implantable medical device of claim 19, wherein the battery comprises at least one of a Li/CF_(x)—CSVO, Li/CSVO, Li/CF_(x), Li/MnO₂, Li/l₂, and Li/SOCl₂ battery.
 21. The implantable medical device of claim 18, wherein the second power source comprises a rechargeable battery.
 22. The implantable medical device of claim 21, wherein the rechargeable battery comprises at least one of a lithium-ion and a nickel/metal-hydride battery.
 23. The implantable medical device of claim 18, further comprising: a switch to couple the first power source to the communication circuit upon occurrence of a first predetermined event.
 24. The implantable medical device of claim 23, wherein the first and second power sources each have a remaining power level associated therewith, the device further comprising: a sensor coupled to the first and second power sources to sense the remaining power level of at least one of the first power source and second power source.
 25. The implantable medical device of claim 24, wherein the first predetermined event includes the sensor sensing the remaining power level of the second power source being below a remaining power level threshold.
 26. The implantable medical device of claim 24, wherein the switch couples the second power source to the control circuit upon occurrence of a second predetermined event.
 27. The implantable medical device of claim 26, wherein the second predetermined event includes the sensor sensing the remaining power level of the first power source being below a remaining power level threshold.
 28. A method for incorporating a power source in an implantable medical device, comprising the steps of: providing power to a control circuit by a first power source, the control circuit obtaining physiological data of a patient in which at least the control circuit is implanted; providing power to a communication circuit by a second power source; and transmitting the physiological data from the communication circuit to an external device.
 29. The method of claim 28, further comprising: sensing a remaining power level of the second power source; determining if the remaining power level has fallen below a predetermined threshold; and providing power to the communication circuit by the first power source in response to determining that the remaining power level has fallen below the predetermined threshold.
 30. The method of claim 28, further comprising: sensing a remaining power level of the first power source; determining if the remaining power level has fallen below a predetermined threshold; and providing power to the control circuit by the second power source in response to determining that the remaining power level has fallen below the predetermined threshold. 